I am not aware of any frame diagram for any Airstream trailer. You will have to pull out the old floor and have a welder scab or replace metal as necessary.
I put new floors in a 1981 22' Excella II trailer. The main rails were 3" "C" channel and of course outriggers but luckily the frame was only rusty but intact. Your trailer will likely have thicker rails/beams.
Make sure you get the new floor up into the bottom channel under the wall and bolted down with elevator bolts. Not the most fun job.
Steve, Christy, Anna and Phoebe (Border Collie)
1994 Classic 30'11" Excella - rear twin
2009 Dodge 2500, 6 Speed Auto, CTD, Quad Cab, Short Bed
Hensley Arrow hitch with adjustable stinger
WBCCI # 3072